1-cyanobicyclo [4.2.0] octa-2, 4-dienes and their synthesis



Patented Sept. 3, 1957 l-CY AN OBICYCLO[4.2.0]OCTA-2,4-DIENES AND THEIRSYNTHESIS Donald Emory Ayer, Bradford, N. H., and George Hermanu Buchi,Cambridge, Mass, assignors, by direct and mesne assignments, to E. I. duPont de Nemours and Company, Wilmington, DeL, a corporation of DelawareNo Drawing. Application January 11, 1957, Serial No. 633,524

8 Claims. (Cl. 260-465) l-cyanobi- 3 8 -rl- 1/2\3CR R! wherein R ishydrogen, a lower alkyl group, i. e., an alkyl group of up to six carbonatoms, or a nitrile group, with not more than one R being nitrile, R andR are hydrogen atoms or lower alkyl groups, as defined, and R ishydrogen or an -R -0R*, -C0R or ()COR group, R being lower alkyl asdefined. The total number of carbons in all substituent groups should benot over 48.

The products of this invention are prepared by contacting a benzonitrileof the formula with an ethylenically unsaturated compound of the formulawherein R, R, R and R have the significance given above, in the presenceof ultraviolet light.

The process of this invention is conveniently carried out by placing amixture of a benzonitrile and an ethylenic compound of the formulasabove in a vessel of a type which allows the reaction mixture to beirradiated by ultraviolet light. The light can be provided by either aninternal or external ultraviolet source. If an external source of lightis used, the vessel is constructed of a material which is transparent toultraviolet light, e. g., quartz or a borosilicate glass containingabout 96% combined silica. If an internal source of light is used, thevessel can be constructed of ordinary glass or of metal. A convenientsource of ultraviolet light is a mercury resonance are produced in aquartz coil which can be immersed in the reaction mixture.

The reaction of this invention is not known to occur in the absence ofultraviolet light. Thus if a reaction mixture is made up in a Pyrex"vessel, substantially opaque to ultraviolet radiation, and an externalsource of ultraviolet light is employed, no reaction takes place.

In some cases when an easily polymerized ethylenic compound is beingused as one of the reactants, a layer of polymer forms on theultraviolet light-irradiating coil. In such cases it is desirable tointerrupt the irradiation periodically to remove the polymer adhering tothe coil.

A convenient wave-length range for the ultraviolet light is betweenabout 1850 A. and 3000 A. but other ultraviolet frequencies can beemployed as well.

The relative proportions of reactants employed are not critical.Proportions ranging from 1 to 3 equivalents of the ethylenic compound toone equivalent of benzonitrile give satisfactory results, but otherproportions can be used if desired.

The reaction temperature and pressure are likewise not critical.Addition of the ethylenic compound to the benzonitrile takes place atordinary temperature, i. e., 2030 C. However, higher or lowertemperatures can be used if desired, e. g., temperatures ranging fromthe melting point of the higher melting reactant to the boiling point ofthe lower boiling reactant. Ambient atmospheric pressure, beingconvenient, will often be employed but superatmospheric andsubatmospheric pressures are also operable.

Irradiation time is not too critical but, since the yield is roughlyproportional thereto, will generally be rather long. Several days ofirradiation are generally employed. The intensity of the ultravioletlight also affects yield to some extent but generators such as themercury resonance are mentioned above give acceptable results inreasonable lengths of time.

The starting materials used in the process of this invention can be thegrades of benzonitriles and ethylenic compounds of good qualityavailable commercially. In some cases it is desirable to redistill thereactants just prior to their use.

In the preferred manipulations of the process, the reaction vessel ischarged with the reactants and the free space thereabove swept out withan inert gas such as nitrogen. The vessel is closed and the reactantsirradiated for several days with ultraviolet light. When the irradiationis completed, the 1-cyanobicyclo[4.2.0]octa- 2,4-diene is generallyisolated in a distillation procedure.

When the ethylenic reactant is a low-boiling material, any excess orunreacted portion of this reactant may be removed at the end of theirradiation period by evaporation. The residue can then be subjected tofractional distillation to remove unreacted benzonitrile and to isolatethe l-cyanobicyclo[4.2.0]octa-2,4-diene. The cyanobicyclo-octadiene canoptionally be subjected to purification treatments, e. g., by treatmentwith aqueous inorganic acids to remove basic impurities, and thendistilled.

There follow some nonlimiting examples which illustrate both the processand the product of the invention in greater detail. In these examples,unless otherwise specified, the pressure is substantially ambientatmospheric and the temperature essentially that of the room or slightlylower, i. e., as determined by a water jacket. Reduced pressures aregiven in terms of mm. of mercury.

Example 1 CN CN H H C CH3 G on. s no G C CH hu HaC-(f C \fli G) 3 HH3CC--C\ /Ull l O OH; H H

An ultraviolet irradiator of the type described by Kharasch andFriedlander in J. Org. Chem. 14, 245 (1949) fitted with a mercuryresonance arc and a water jacket is charged with 145 cc. of benzonitrileand 460 cc. of 99% Z-methyI-Z-butene. The system is flushed withnitrogen and then the inlet and outlet to the reaction vessel areclosed. The mercury resonance arc is operated at about 9000 volts and 30milliamperes for 26 days. Unreacted olefin is evaporated from themixture, and the remainder is distilled through a spinning band columnat reduced pressure. After 110 cc. of benzonitrile is recovered, thereis obtained 9.5 g. of impure 7,8,8-trimethylbicyclo[4.2.01octa 2,4 diene1 carbonitrile, boiling at 56-68 C./0.1 mm.

The crude product is dissolved in diethyl ether and extracted with 5%hydrochloric acid to remove basic impurities. Evaporation of the ethersolution yields 7.6 g. of yellow liquid. On distillation of this liquidthrough an efficient fractionating column, there is obtained 6 g. ofcolorless liquid boiling at 42-44 C./0.02 mm., and having a refractiveindex, rid, of 1.4970.

Analysis.Calcd. for C12H15N: C, 83.19%; H, 8.73%; N, 8.09%. Found: C,83.08%; H, 8.65%; N, 8.21%.

The ultraviolet spectrum has an absorption peak at 274 millimicrons(2:3370); and a minimum at 227 millimicrons (2:865). The infraredabsorption spectrum exhibits a sharp band at 4.5 microns.

Various derivatives of the product of (a) may be prepared as follows:

(b) A solution of 0.79 g. of 7,8,8-trimethylbicyclo-[4.2.0]octa-2,4-diene-l-carbonitrile in acetic anhydride is hydrogenatedat room temperature and atmospheric pressure in the presence of 100 mg.of platinum oxide. The uptake of hydrogen beyond 1 mole-equivalent isslow and the reaction is continued for 72 hours with two subsequentadditions (100 mg. each) of fresh catalyst. The solution is filtered andthe acetic anhydride is decomposed by stirring the solution for one hourwith an equal volume of water. The acid is neutralized with solidpotassium hydroxide and the aqueous solution is extracted with ether.The ether solution is washed with 5% hydrochloric acid and water.Evaporation of the ether gives 0.83 g. of a white, sticky solid.Crystallization from petroleum ether-benzene gives colorless rods, M. P.139- 140 C., of N-acetyl-(7,8,8)-trirnethy1bicyc1o[4.2.01-octane-l-methylamine:

CHzNHGOCH:

C, 75.28%; H, Found: C, 74.83%; H, 11.15%;

dicarboxylate containing 10 mg. of hydroquinone is heated at 60 C. undernitrogen for 48 hours. Most of the benzene evaporates, leaving anorange-yellow oil which is dissolved in 2 cc. of benzene. Addition of 5cc. of petroleum ether causes 1 g. of white material, M. P. 117 C., toprecipitate out. Crystallization from benzene-petroleum ether givescolorless, cubical crystals, melting at l21122 C., of the Diels-Alderadduct:

CN H CH3 l i (5600011; U cocoon. OH

Analysis-Calm. for C1aH21O4N: C, 68.55%; H, 6.71%. Found: C, 68.77%; H,6.69%.

(d) A 0.7-g. sample of the Diels-Alder adduct described in the precedingparagraph is placed in a micro- Claisen flask equipped with a nitrogencapillary. Two receivers are used in series, the first ice-cooled, thesecond cooled in a mixture of acetone and solid carbon dioxide. A vacuumof 1 mm. is applied to the system. The Claisen flask is immersed in anoil bath heated to 200 C. Decomposition occurs immediately, producingtwo fractions: (1) a colorless oil which distills into the ice-cooledreceiver, amounting to 0.267 g. and having a refractive index, 11 of1.5095; and (2) a liquid which condenses in the acetone-solid carbondioxide-cooled receiver, amounting to 0.17 g. and having a refractiveindex, 11 of 1.4464.

A solution of 0.115 g. of fraction (1) in ethanol is added to a solutionof potassium hydroxide in aqueous ethanol and refluxed four hours. Thesolution is aciditied and evaporated to dryness in vacuo. Sublimation at200 C. and atmospheric pressure gives 60 mg. (67%) of phthalicanhydride, M. P. 130131 C. A mixed melting point with an authenticsample of phthalic anhydride is 130-131 C. Fraction (1) exhibits aninfrared absorption spectrum nearly identical with that of pure dimethylpure dimethyl phthalate.

Fraction (2) exhibits a strong peak at 4.55 microns in the infraredspectrum, and is 3,4,4-trimethyl-1-cyclobutenecarbonitrile,

An acetic anhydride solution of fraction (2) is hydrogenated at roomtemperature and atmospheric pressure in the presence of mg. of Platinumoxide. After 48 hours the hydrogenation is complete; the solution isthen filtered, excess acetic anhydride decomposed with water, and thesolution neutralized with solid potassium hydroxide. Ether extractiongives a yellow oil which is dissolved in petroleum ether andchromatographed on neutral alumina (activity I). The material elutedwith 1:1 petroleum ether/benzene is distilled at 0.06 min. with a bathtemperature of 100 C. giving 60 mg. of colorless oil. This product hasthe formula:

Analysis.-Calcd. for CmHmNO: C, 70.96%; H, 11.32%; N, 8.23%. Found: C,70.36%, 70.59; H, 11.41%, 11.47; N, 7.65%.

The infrared spectrum of this product exhibits bands characteristic fora mono-substituted amide (3.0, 6.06, and 6.6 microns).

Example 2 the reactants listed in the following table, the specific ONON cyanobicyclooctadiene products given in the table are H l H obtained.CHaGO-O C Table CHCO 0 \CH hu Hl- \CH g H & Reaetants H \C% Products H HNltrlle Ethylenle Compound An ultraviolet light irradiator of the typeused in example 1 is charged with 78 g. of vinyl acetate andp-Tolunltrile l-octene B-n-hexyl-4-metl1ylblcyclo 34 g. of benzonitrile.The mixture is irradiated with a tgf -fltggf mercury resonance arcoperated at 9000 volts and 30 2.3-xylonitri1e propene2,3,S-trlmethylblcyclo [4.2.0]- milliamperes for F days at roomtemperature; f 3,4,6-trimethylethylene if F$ii$iiil$iilli$ acted vinylacetate is evaporated from the reaction Il'llX- benzonitrile. oct&-2,4-dlene-l-earboniture and the residue is distilled at reducedpressure. After Bemomtmem 2 4 4 t .1 h 1 1 recovery of unreactedbenzonitrlle, there ls obtained a pentene. pyD-bicyclo[4.2.0]-octa-2,4-slightly yellow liquid, B. P. 105110/0.0 4 mm. and Do mummy! 32533153535"{llg; n 1.510. This compound is 8-acetoxyblcycloi4.2.0] D k gm l It 2-d t nelm fil nifrllg octa-2,4-diene-l-carbonitrile. me Y acrya g l fififgig jg gj Analysis, calcd, for CnHuOgN; C, 69,827 H, Pnthalonttrile2-methyl-2-butene. 7,8,8-trimcthylblcyclo[4.2.0]- s.ss%; N, 7.40%.Found: c, 69.99%; H, 6.03%; N, $535? 753%, Terephthal0nitrlle l-buteneB-etllylblcyclo[4.2.0]-oeta 2,4- The infrared absorption spectrum ofthis compound hene'l'4'dmrbomtrne' exhibits a split band in the nitrileregion (4.46 and 4.49 microns) and bands characteristic for an acetateat 5.73 Products of mvennol? are useful as mtermed" and 811 microns ates1n the synthesis of substltuted cyclooctatetraenes.

Example 3 For example, when 8 acetoxybicyclo[4.2.0] octa-2,4- 6N ONdlene-l-carbonltrlle is heated it is converted to bicyclo[4.2.0]octa-2.4,7-triene l carbonitrile and cyclooctagtetraene-l-carbonitrilc. The resulting substituted cyclo- Hoctatetraenes are in turn useful as analogues of phar- OrHrO f CH(limo-CA3 CH maceuticals in which the benzene rings are replaced by E 4cyclooctatetraene substituents. The products of this invention are alsouseful as diencs for the synthesis of poly- H H functional Diels-Alderadducts which are useful as co- A mixture of 515 g of benzonitrile and36.1 g of monomers and ascrosslinking agents as well as for the ethylvinyl ether which has been freshly distilled from synthesls ofmsecucldes chlprdane type- P sodium is irradiated in apparatus of thetype used in the ample 2 prcfdflcts of thls mventon F be clllormatsdpreceding examples with a mercury resonance are oper to formlnsectlcldes whlch can be used lnemulsliiable olls ated at 9000 voltsand 30 milliamperes for 44 hours. At as wettable Powders to control manyInsects Including; the end of this time the excess vinyl ether isevaporated f Posqulmes, Furthemwre. thfi Products of thls from thereaction mixture and the residue is distilled Y f useful the Pmdu'?nonof Polymers 6011' through a spinning band column. After separation oftamfng l funcuoflsunreacted benzonim'le, there is obtained 05 g. of a 45Since obvlousmodlficatlonsln the invention will occur colorless liquidboning at 57 3 0 05 mm and hav. to those skilled ln the art, We proposeto be bound solely ing a refractive index, n of 1.5158. This is8-ethoxyby the I 'P F 31311115- bi l mgp -2 4 p i The embodu'nents ofthe invention in which an exclu- 1 1 f O C, 75.40% H sive property orprivilege is claimed are defined as fol- 7.4s%; N, 7.99%. Found: c,75.61%; H, 7.46%; N, lows: 1. A l-cyanobicyclo[4.2.0]octa-2-,4-diene ofthe for- The ultraviolet absorption spectrum has a maximum mula at 277millimicrons (2:3662) and a minimum at 234 (3N millimicrons (2:2360). 55R The examples have illustrated the process and prod- (l; nets of thisinvention by specific reference to certain l-cyanobicyclooctadienes.However, the products of this R invention include otherl-cyanobicyclooctadienes of the R formula R R ON H -R i PM t \H is a Rwherein: (l) R is a member of the class consisting of R hydrogen, loweralkyl groups, and the nitrile group, not H more than one R beingnitrile; (2) R and R are members of the class consisting of hydrogen andlower alkyl l f groups; (3) R2 is a member of the class consisting ofwherein R, R R and R have the significance given hereinbefore. Thus,when the benzonitrile and the ethylenic compounds of the examples arereplaced by R OR COR and OCOR R being a lower alkyl group; and (4) thetotal number of carbon atoms in all substituent groups is not over 48.

2. 7,8,8 trimethylbicyclo[4.2.0]octa 2,4-diene-1-carbonitrile.

3. 8 acetoxybicyclo[4.2.0]octa 2,4 diene 1 carwherein R, R R and R areas defined in claim 1, in the bonitrile. presence of ultraviolet light.

4. 8 ethoxybicyclo[4.2.0]octa 2,4 diene 1 car- 6. The method ofpreparing the compound of claim 2 bonitrile. which comprises reactingbenzonitrile with 2-methy1-2- 5. The method of preparing a compound ofclaim 1 5 butene in the presence of ultraviolet light. which comprisesreacting a benzonitrile of the formula 7. The method of preparing thecompound of claim 3 ON which comprises reacting benzonitrile with vinylacetate in the presence of ultraviolet light. 8. The method of preparingthe compound of claim 4 R-C CR 10 which comprises reacting benzonitrilewith ethyl vinyl L ether in the presence of ultraviolet light.

i No references cited. with an ethylenically unsaturated compound of thefor- 15 mula

1. A 1-CYANOBICYCLO(4.2.0)OCTA-2-,4-DIENE OF THE FORMULA